Retinoic acids and its natural and synthetic analogs exact a wide variety of biological effects. They have been found to affect cellular growth and differentiation and are promising agents for the treatment of several cancers.
U.S. Pat. No. 4,808,631 discloses compounds of the formula ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, and R.sup.5 independently are hydrogen, alkyl, or C.sub.3-7 cycloalkyl or two adjacent residues R.sup.1 to R.sup.5 taken together with adjacent carbons of the phenyl ring form a 5-7 membered ring optionally substituted by one or more lower alkyl groups; X is --NR.sup.7 --CO-- or --CO--NR.sup.7 --; R.sup.6 is hydroxy, lower alkoxy or --NR.sup.8 R.sup.9 ; and R.sup.7, R.sup.8 and R.sup.9, independently, are hydrogen or lower alkyl, and where R.sup.6 is hydroxy, their pharmaceutically usable salts for the treatment of inflammatory and rheumatic diseases.
U.S. Pat. No. 4,703,110 discloses compounds of the formula ##STR3## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 may be the same or different, each represents hydrogen, middle and lower alkyl and/or cycloalkyl having 3-7 atoms, with the proviso each cannot be hydrogen simultaneously, and both neighboring substituents may be combined with each other to form a ring having 5-12 carbon atoms, R.sub.6 represents hydroxyl, lower alkoxyl, lower alkylamino of the formula --NR.sub.7 'R.sub.8 ', wherein R.sub.7 ' and R.sub.8 ' each represent hydrogen or lower alkyl, X represents a group of the formula: ##STR4## wherein R.sub.7 and R.sub.8 represent hydrogen or lower alkyl. Such compounds are said to be capable of inducing the differentiation of premalignant and malignant cells to morphologically and functionally mature cells which cannot proliferate further and can therefore be used in the therapy of premalignant and malignant diseases.